Method and apparatus for locking a manhole cover

ABSTRACT

A manhole cover lock includes a lock body which is mounted to the cover and a lock arm mounted for rotation relative to the lock body. The lock arm is mounted to a pin which is positioned in a passage through the lock body. The pin has a specially shaped head for engagement by a special tool. A nut is threaded onto a bottom end of the lock body at a bottom side of the cover. The lock arm can be rotated with the pin from an unlocked position to a locked position, the arm in the locked position rotated under or into engagement with a support or other structure which underlies the manhole cover. The lock arm is retained in its locked position by being biased upwardly to a position where tabs on the lock arm fit into a slot in the lock body.

FIELD OF THE INVENTION

The present invention relates to methods and devices for locking manhole covers to prevent their removal.

BACKGROUND OF THE INVENTION

Manhole covers are utilized for a variety of purposes. Often, access points to sewers and underground utilities are provided via passages leading to the surface of the earth. It is desirable to close those passages when they are not in use in order to prevent people, animals and the like from falling into the passages.

Manhole covers are frequently used for this purpose. Manhole covers are typically iron or steel plates which are located over the access hole or passage. FIG. 1 illustrates one example of a manhole cover. The particular manhole cover which is illustrated is generally circular in shape and has opposing top and bottom sides. The top side may display ornamentation, such as one or more designs, to make it aesthetically pleasing. In addition, one or more small holes or depressions may be located in the manhole cover.

FIG. 2 illustrates one exemplary use of a manhole cover. As illustrated, a passage P in the earth leads to an opening O. In the example illustrated, the opening is in a street surface S. A frame F is located in the street S. The frame F defines a support surface or flange upon which the manhole cover C may rest. Preferably, the frame F is set into the street surface S a sufficient distance that the top of the cover C is flush with the street when the cover is supported by the frame F.

The manhole cover is simple to remove and install, in that the cover is maintained in position on the frame simply by the weight of the cover. The cover may be removed, for example, by placing a hook into either or both holes in the cover and then lifting the cover upward off of the frame.

Unfortunately, because the manhole cover is maintained in position by gravity only, manhole covers are often undesirably removed. For example, a vehicle passing over a manhole cover may cause the cover to spring upward off of its frame, thus partially or entirely uncovering the opening O. In the case of sewers, excessive fluid flow, such as in the event of a thunderstorm with significant precipitation, may cause the manhole cover to be lifted out of position. In addition, manhole covers are often stolen for their value in metal.

A method and apparatus for selectively maintaining or locking a manhole cover is desired.

SUMMARY OF THE INVENTION

The invention is a method and apparatus for locking a manhole or similar cover in a fixed position, such as over an opening or hole. The apparatus has particular utility to generally solid, round manhole covers.

One embodiment of the invention is a cover lock for use with a manhole cover. The cover lock comprises a lock body for mounting to a cover, and a lock arm mounted for rotation relative to the body and into an out of engagement with a cover supporting structure.

In one embodiment, the lock body has a first end and a second end and a passage there through. The lock arm is mounted for rotation relative to the lock body. In a preferred embodiment, the lock arm is connected to a pin which is positioned in the passage through the lock body. The pin has a head located at the first end of the lock body. The lock arm is mounted to the second end of the pin and is positioned at the second end of the lock body. The lock arm moves with the pin when the head of the pin is engaged and rotated.

In a preferred embodiment, the cover lock includes means for selectively locking the lock arm to the lock body and preventing relative rotation thereof. In one embodiment, at least one slot is located in the second end of the lock body for engagement with one or more tabs which extend outwardly from the lock arm. In addition, means are provided for biasing the lock arm upwardly whereby the one or more tabs engage the at least one slot when the tab(s) and slot(s) are aligned. In one embodiment, this means comprises at least one spring mounted under the head of the pin.

In use, the cover lock is mounted to the manhole or other cover. The lock body is placed in a passage through the manhole cover. In a preferred embodiment, the lock body has an enlarged cap at the top end, and that cap is positioned in an enlarged portion of the passage through the manhole cover, whereby the top of the lock body is generally flush with a top of the manhole cover.

In one embodiment, the lock body is secured to the manhole cover to prevent its removal therefrom and its rotation relative thereto. In one embodiment, a nut is threaded onto the bottom end of the lock body at the bottom side of the manhole cover, thus preventing removal of the lock body from the top of the manhole cover. A pin is preferably placed into the cap of the lock body and into engagement with the manhole cover at the top side thereof in order to prevent rotation of the lock body relative to the manhole cover.

The pin is positioned in the passage through the lock body and the lock arm is connected to the pin at the bottom end of the lock body, and thus at the bottom side of the manhole cover. The manhole cover is then configured to be mated with its support structure.

In use, the manhole cover with lock is placed on a support structure, such as a frame having an outwardly extending flange. The lock arm is rotated from an unlock to a locked position. This is effected by rotating the pin.

In one embodiment, a head of the pin has a special configuration for engagement by a special tool. In a preferred configuration, the head has a triangular shape, the farthest outer portions thereof located close to the walls of the passage through the lock body which houses the pin. In use, the special tool is connected to the head of the pin at the top side of the manhole cover. The pin is rotated, thus rotating the lock arm.

The lock arm is rotated until at least a portion of the arm is positioned beneath or otherwise engages a portion of the support or other structure beneath the manhole cover. Preferably, the lock arm is then locked into that position by the spring which engages the pin (such as by being between the lock body and the head of the pin) biasing the pin, and thus the lock arm, upwardly into a position where the tab(s) on the lock arm engage the slot(s) in the lock body. At that time, upward movement of the manhole cover is prevented because the lock arm engages or hits the underlying support structure.

To unlock the lock arm, the pin is pressed downwardly, thus moving the tab(s) on the lock arm of engagement with the slot(s) on the lock body. The pin is then rotated, thus rotating the lock arm, until the lock arm disengages the support or other structure. At that time, the manhole cover can be lifted upwardly.

Further objects, features, and advantages of the present invention over the prior art will become apparent from the detailed description of the drawings which follows, when considered with the attached figures.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a manhole cover in accordance with the prior art;

FIG. 2 is a cross-sectional side view of a manhole cover and supporting frame as used in the prior art;

FIG. 3 is an exploded view of a cover lock in accordance with one embodiment of the invention;

FIG. 4A is a top view of a pin of the cover lock illustrated in FIG. 3;

FIG. 4B is a side view of the pin illustrated in FIG. 4A;

FIG. 5 is a side view of a lock body of the cover lock illustrated in FIG. 3;

FIG. 6 is a top view of a lock arm of the cover lock illustrated in FIG. 3;

FIG. 7 is a cross-sectional side view of the cover lock of the invention when assembled;

FIG. 8 illustrates a cover lock of the invention as mounted to a manhole cover, the cover lock shown in a locked position; and

FIG. 9 illustrates the cover lock of FIG. 8 in an unlocked position.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a method and apparatus for locking or securing a manhole or similar cover. In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.

In general, the invention is a method and apparatus for securing a manhole or similar cover. The apparatus comprises a lock for association with a manhole cover. The lock is configured to selectively engage a frame or other manhole cover support, thus selectively securing the cover to the support and preventing its removal therefrom. As described below, the lock is particularly suited to use with “plate” type manhole covers, such as generally closed or solid circular covers.

One embodiment of the invention will be described with reference to FIGS. 3 and 7. FIG. 3 illustrates, in exploded view, a manhole cover lock 20 in accordance with an embodiment of the invention. FIG. 7 shows the cover lock 20 in cross-sectional view, when assembled. In general, the lock 20 comprises a lock body 22, a securing nut 24, a lock arm 26, and a control pin 28.

The lock body 22 will be described with reference to FIG. 5. In one embodiment, the lock body 22 is generally cylindrical in shape, and has a top or first end 30 and a bottom or second end 32. The lock body 22 defines a cap portion 34 at the top end 30. The cap portion 34 preferably has a generally planar top surface which coincides with the top of the lock body 22. When the cap portion 34 is generally cylindrical in shape, the cap portion 34 preferably has a first diameter.

A main portion 36 of the lock body 22 is located below and extends from the cap portion 34. In a preferred embodiment, the main portion 36 of the lock body 22 is generally cylindrical in shape and has a second diameter which is less than the first diameter of the cap portion 34. As a result, a ledge or step 38 is formed at the intersection of the main portion 36 of the lock body 22 and the cap portion 34. Where the main portion 36 and cap portion 34 are both cylindrical in shape, the ledge or step 38 extends around the entire lock body 22.

The lock body 22 also includes a mounting portion 40. In one embodiment, the mounting portion 40 has a third diameter which is less than the second diameter of the main portion 36 of the lock body 22. In one embodiment, the main portion 36 and mounting portion 40 are separated by a groove 42. The groove 42 may comprise a section of the lock body 22 having a smaller diameter than both the main portion 36 and mounting portion 40 of the lock body 22.

In one embodiment, the mounting portion 40 is configured to accept one or more members for selectively connecting the lock body 22 to a manhole cover. As disclosed below, in one embodiment, such members may comprise the locking nut 24. In that instance, the mounting portion 40 is preferably externally threaded.

At its second end 32, the lock body 22 defines a second mounting portion or section 44. As disclosed below, in one embodiment, the second mounting portion 44 accepts the lock arm 26. In such an embodiment, the second mounting portion 44 preferably defines a locking channel or slot 46 for accepting at least a portion of the lock arm 26.

As disclosed below, in use, the lock body 22 is associated with a manhole cover. In one embodiment, the cover lock 20 includes means for selectively securing the lock body 22 to a manhole cover. In one embodiment, this means includes at least one securing pin (not shown) which is configured to engage the lock body 22 and the manhole cover. In one embodiment, the pin is configured to be located in a passage 48 through the cap portion 34 of the lock body 22 at one location along the flange 38, whereby the pin may also extend into a mating passage formed in the manhole cover. As described below, the pin is effective in preventing rotation of the lock body 22 relative to the manhole cover.

In a preferred embodiment, a passage 50 extends through the lock body 22 from its top end 30 to its bottom end 32. In one embodiment, the passage 50 extends along a centerline of the lock body 22. Preferably, the passage 50 has a first portion 52 and a second portion 54 of different sizes. In an embodiment where the passage 50 is generally cylindrical in shape, a diameter of the first portion 52 is preferably larger than a diameter of the second portion 54. Preferably, the first portion 52 extends from the top end 30 into the lock body 22 a first distance (which, as described below, accepts a head portion of the pin 28 and movement thereof) and the second portion 54 extends from the first portion 52 to the second end 32 of the lock body 22 (and is sized to accept a stem portion of the pin 28).

The lock body 22 may be constructed from a wide variety of materials and using a wide variety of techniques. In one embodiment, the lock body 22 is constructed of metal, such as iron or steel, and is more preferably constructed of stainless steel or other corrosion-resistant materials. The lock body 22 may be constructed in a molding and/or machining process or in other manners.

As will be described in more detail below, in one embodiment, the lock body 22 may be connected to and disconnected from, a manhole cover. In one embodiment, means are provided for selectively locking the lock body 22 to a manhole cover. In a preferred embodiment, this means comprises the locking nut 24 configured to engage the lock body 22.

Referring to FIG. 3, the locking nut 24 preferably comprises an annular lock body 22 having a threaded interior surface. The threads defined by the interior surface are configured to mate with the threads defined on or by the exterior of the lock body 22. One or more slots or notches 56 may be located in an exterior portion of the locking nut 24, such as for engagement of a tool for use in tightening or loosening the nut 24.

As indicated, the cover lock 20 preferably includes a lock arm 26. As described below, the lock arm 26 is preferably configured to be mounted to the lock body 22 at the second or bottom end 32 thereof.

The lock arm 26 will be described with reference to FIGS. 3 and 6. As illustrated therein, the lock arm 26 preferably has a first end 58 and an opposing end 60. Though the exact shape of the lock arm 26 may vary, in one embodiment, it is generally elongate and rod-shaped. In that embodiment, the lock arm 26 may have a generally rectangular or square cross-sectional shape, and the width and height of the arm are much less than the length of the arm from end-to-end. Preferably, the lock arm 26 has sufficient length which permits it to be connected to the lock body 22 and extend therefrom into engagement with a frame or other support of the manhole cover, in the manner described in more detail below.

As illustrated, the lock arm 26 has a pair of opposing sides between the ends 58,60, and a top and a bottom. In the generally rectangular cross-sectional shape illustrated, the sides lie in planes which are generally parallel to, but offset from one another, as do the top and bottom.

In one embodiment, means are provided for selectively retaining the lock arm 26 in a fixed position. As described below, this position is preferably a position in which the lock arm 26 engages a manhole cover frame or other support element. In one embodiment, this means comprises a pair of raised tabs 62 a,b. In a preferred embodiment, these tabs 62 a,b extend from the top of the lock arm 26 and are positioned and sized to engage the portions of the slot 46 at opposing sides of the bottom end 32 of the lock body 22. In the embodiment where the slot 46 is generally rectangular in shape, so are the mating tabs 62 a,b.

Preferably, the lock arm 26 is mounted for rotation relative to the lock body 22. In a preferred embodiment, the lock arm 26 is mounted to the pin 28, in a manner described in more detail below.

The pin 28 will now be described with reference to FIGS. 3, 4A and 4B. The pin 28 has a top or first end 64 and an opposing bottom or second end 66. The pin 28 has a head 68 located at the top end 64. In a preferred embodiment, as illustrated in FIG. 4A, the head 68 is configured for engagement by a tool to permit the pin 68 to be rotated. In a preferred embodiment, the head 68 has a unique shape, thus permitting its engagement only with a particular mating tool. As illustrated in FIG. 4A, the head 68 is generally triangular in shape. As described in more detail below, the head 68 is preferably sized so that the outer-most portions of the head 68 are located adjacent the wall of the top portion 52 of the passage 50.

In one embodiment, a main portion of a lock body 22 of the pin 28 below the head 68 is generally cylindrical in shape and sized to fit within the reduced diameter, second portion 54 of the passage 50 through the lock body 22.

As described above, the lock arm 26 is preferably mounted to the pin 28. In one embodiment, a passage 70 extends into the pin 28 at the second end 66 thereof. A corresponding passage 72 extends through the lock arm 26. As best illustrated in FIG. 3, a bolt 74 preferably extends into the passage 72 through the lock arm 26 and into engagement with the passage 70 in the pin 28. In such an embodiment, the passages 70,72 are preferably internally threaded for engaging mating threads on the bolt 74.

In a preferred embodiment, means are provided for preventing the lock arm 26 from rotating relative to the pin 28. As illustrated in FIG. 4B, a slot 76 is located at the second end 66 of the pin 28. A mating tab 78 extends upwardly from the top of the lock arm 26. The tab 78 is preferably sized and shaped to fit within the slot 76 in the pin 28.

Of course, the lock arm 26 might be connected to the pin 28 in a variety of other manners. For example, the lock arm 26 could be welded to the pin 28.

Means are preferably provided for biasing the lock arm 26 upwardly into its locking position with the lock body 22. Referring to FIG. 3, this means preferably comprises at least one spring 80. As illustrated, the spring 80 is a coil spring which is configured to be mounted over the cylindrical lock body 22 portion of the pin 28. The spring 80 preferably biases the pin 28 upwardly relative to the lock body 22, thus biasing the lock arm 26 upwardly into a position in which the locking tabs 62 a,b thereon engage the slot 46 in the second end 32 of the lock body 22, in a manner described in more detail below.

Like the lock body 22, the other components of the cover lock 20 may be constructed in various manners of various materials. For example, the lock arm 26 and pin 28 may be constructed in molding or machining processes. Preferably, the components of the cover lock 20 are constructed of durable and, most preferably, corrosion-resistant materials, such as steel, stainless steel, brass or the like.

Use and assembly of the cover lock 20 will now be described in detail. Referring to FIGS. 8 and 9, the cover lock 20 is particular suited to use with a manhole cover M. As described above, such covers M may have a variety of configurations. The cover lock 20 is particularly suited to use with manhole covers M which are generally solid, round in shape, and constructed of metal.

The lock body 22 of the cover lock 20 is preferably mounted to the manhole cover M. Preferably, the lock body 22 is located in a passage or opening formed in the cover M. The cover lock 22 may be utilized with manhole covers M which are specially configured, such as by being formed in a molding process with a passage for the lock body 22. However, the cover lock 20 has applicability to “retro-fit” applications where a passage is formed in an existing manhole cover M.

With reference to FIG. 8, in preferred embodiment, the passage P in the manhole cover M has a first enlarged portion and a second narrower portion. The enlarged portion of the passage P is configured to accept the cap 34 portion of the lock body 22, while the narrower portion is configured to accept the main portion 34 of the lock body 22. Thus, when located in the passage P, the cap 34 is supported by the manhole cover M, with the first end 30 of the locking body 22 at the cap 34 being generally flush with a top of the manhole cover M. The main portion 36 of the lock body 22 extends through the passage P in the manhole cover M, such that the second end 32 of the lock body 22 extends from the second or bottom side of the manhole cover M.

Preferably, the lock body 22 is secured to the manhole cover M to prevent movement of the lock body 22 with respect thereto and removal of the lock body 22 therefrom. A pin 82 is preferably placed through the passage 48 in the cap 34 of the lock body 22. The pin 82 preferably passes into a mating passage or aperture in the manhole cover M (which may be formed by molding, machining or the like). The pin 82 may be threaded or, in a preferred embodiment, a rod which is press-fit into engagement with the lock body 22 and manhole cover M.

In addition, the nut 24 is threaded onto the mounting portion 40 of the lock body 22. The nut 24 is thus located on the lock body 22 at the bottom side of the manhole cover M, as illustrated in FIGS. 8 and 9.

The lock arm 26 is connected to the pin 28. In a preferred embodiment, the spring 80 is located on the pin 28 and the pin 28 is then placed into the passage 50 through the lock body 22, as illustrated in FIGS. 3 and 7. The lock arm 26 is then connected to the pin 28 with the bolt 74. Of course, the tab 78 on the lock arm 26 is located in the slot 76 in the pin 28 during this process.

The cover lock 20 is then configured for use in locking a manhole cover M, as illustrated in FIGS. 8 and 9. FIG. 8 illustrates the cover lock 20 in its locking position. In this position, the manhole cover M is located on a supporting frame F or other support structure. The lock arm 26 is in a position in which the second or free end 60 thereof is positioned under a portion of the frame F, thus preventing its upward movement. In addition, the lock arm 26 is locked in position relative to the lock body 22, in that the spring 80 has pulled the lock arm 26 upwardly such that the lock tabs 62 a,b on the lock arm 26 are positioned in the slot 46 in the second end 32 of the lock body 22.

Because the second end 60 of the lock arm 26 is located under a portion of the frame F, the manhole cover M can not be lifted upwardly, thus preventing the manhole cover M from being removed.

The manhole cover M can be removed by unlocking the cover lock 20, as illustrated in FIG. 9. The special tool (not shown) is preferably placed into engagement with the head 68 of the pin 28. The pin 68 is pressed downwardly against the force of the spring 80. As the pin 28 is pressed downwardly, the tabs 62 a,b are moved out of the slot 46 in the lock body 22. At that time, the pin 28 can be rotated. As the pin 28 is rotated, the lock arm 26 simultaneously rotates.

Once the arm 26 is rotated a sufficient distance, the second end 60 thereof moves out from under the frame F. The manhole cover M can then be lifted upwardly.

It will be appreciated that the cover lock is located in a position on/in the cover that, when considering the length of the lock arm, permits the lock arm to extend into engagement with the support or other structure. In one embodiment, the cover lock is located near the perimeter of the cover, thus permitting the lock arm to be as short as possible.

It will now be appreciated that one aspect of the invention is a cover lock which may be used to lock a manhole or similar cover. Another aspect of the invention is a locking manhole cover, the cover having a cover lock in accordance with the invention mounted thereto. Yet other aspects of the invention are methods of locking and unlocking a manhole cover from a surrounding structure, thus securing the cover thereto and preventing its removal therefrom, or permitting removal of the cover therefrom.

The cover lock may be used with a variety of covers. The cover lock has particular applicability to a generally “closed” cover (i.e., having a solid top/bottom) where access from the top to the bottom is limited (i.e., the over does not have openings therein or only small openings therein). Such covers may be of a variety of shapes, and are often circular.

Various additional aspects of the invention will now be described. A lock is provided for a manhole or similar cover which can be used with an existing cover (by machining the appropriate passages into an existing cover and connecting the cover lock thereto, for example) or a specially configured cover (such as a cover molded or stamped to include the appropriate mounting passages for the cover lock). The lock works effectively with existing cover support frames, thus eliminating the need to modify the cover support/frame, reducing the cost of retrofitting existing covers to the locking configuration.

The cover lock can be used to secure manhole or similar covers which are mounted in various fashions. FIGS. 8 and 9 illustrate a particular configuration where a supporting frame has an outwardly extending flange. The cover lock could be used with other types of supports or supporting structures, whether they are a frame or simply a surrounding supporting material (such as concrete or the like). In particular, the lock need only rotate into a position where it is below a portion of or otherwise engages the support, whether that portion is a flange or even a slot or the like. In another embodiment, a flange or stop can be mounted to a support structure or material (such as the wall of a concrete conduit which defines the opening over which the cover is located), which flange or stop is then engaged by the lock arm.

In this regard, it is noted that the configuration of the lock arm may vary depending upon the structure of the support it is to engage. For example, if the lock arm is to engage a slot, the free or second end of the lock arm may be generally flat.

In its preferred form, the cover lock has a modular construction, permitting components of the cover lock to easily be manufactured and replaced.

The cover lock has an effective locking configuration, while still permitting the cover lock to be locked and unlocked by authorized parties. In particular, the cover lock can easily be locked and unlocked with a special tool, but not by use of common wrenches or the like. This is due to a number of factors. First, the shape of the head of the pin is unique, thus preventing common tools from easily engaging it. In addition, because the head of the pin is located in the passage through the lock body, it can not easily be engage with “universal” tools such as pipe wrenches or the like. In addition, in order to unlock the cover lock, the pin must not only be pushed downwardly, but it must be rotated. Even if a “universal” tool can be angled into position on the head of the pin to effect rotation of the head, when the user pushes downwardly on the pin to “unlock” the lock arm, the tool will be dislodged due to the small clearance between the outer edge of the head of the pin and the surrounding wall of the passage through the lock body.

Other configurations of the cover lock are contemplated as within the scope of the invention. As described, in the preferred embodiment, means for connecting the lock body to the manhole cover to prevent removal therefrom and/or movement relative thereto preferably comprises the engaging nut and pin. Preferably, the means locking the lock body to the cover are not accessible from the top of the cover, in order to prevent parties from disconnecting the lock body from the cover, thus thwarting the effectiveness of the cover lock (e.g. in the preferred embodiment, the nut 24 is only accessible from the bottom of the manhole cover since the cover is generally “closed” or solid, thus preventing the lock body 22 from being removed when the cover is in its locked condition).

Other means could be utilized, however. For example, the lock body could be welded to the manhole cover once it is mounted thereto. Bolts or similar fasteners could be located at the bottom side of the cover and engage the manhole cover and the lock body. A cotter pin or the like could be passed into the lock body at the bottom side of the manhole cover to prevent upward movement of the lock body.

In one embodiment, instead of the pin having a specially shaped head, the pin could define a specially shaped aperture. The aperture may be configured to mate only with a specially configured male-portion of a tool which then permits rotation of the pin. It is also possible for the pin to be configured as a cylinder or similar lock, wherein a key which is inserted into the pin selectively controls a lock pin which selectively extends into or out of engagement with the lock body, thus controlling whether the pin can be moved.

Other means might be provided for biasing the lock arm upwardly. For example, one or more pins may be spring loaded and mounted to the lock body and press upwardly upon the bottom of the head of the pin. The spring 80 could also be located elsewhere, and/or other types of springs or biasing members could be used to bias the pin 28, and thus the lock arm 26, upwardly.

The means for selectively locking the lock arm 26 to the lock body 22 in a manner preventing relative rotation could also vary. As described, this means comprises one or more tabs extending from the lock arm 26 into engagement with at least one slot 46 in the lock body 22. Alternatively, one or more tabs could extend from the lock body 22 for engagement with one or more slots in the lock arm 26. It is also noted that the tabs and slots need not be formed exactly as illustrated. For example, the slot need not be elongated, but could be a depression or recess slightly bigger than the tab which it is to accept. The tabs could also be formed as pins and the slot could be formed as a passage.

It will be understood that the above described arrangements of apparatus and the method there from are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the invention as defined in the claims. 

1. A locking device for use with a manhole cover comprising: a lock body for mounting to a manhole cover, said lock body having a first end and a second end, said lock body having a passage there through and defining at least one slot at said second end thereof; a pin having a first end and a second end, said pin defining a head at said first end; a lock arm, said lock arm mounted to said pin at said second end of said pin and said lock arm located at said second end of said lock body when said lock arm is connected to said pin, said lock arm rotatable relative to said lock body, said lock arm including at least one outwardly extending tab for engagement with said at least one slot in said lock body; and a spring positioned between said head of said pin and said lock body, whereby said pin is biased upwardly, causing said at least one tab of said lock arm to engage said at least one slot of said lock body when aligned therewith.
 2. The locking device in accordance with claim 1 wherein said lock body has a threaded exterior portion at said second end thereof and including a nut for selectively engaging said threaded portion of said lock body.
 3. The locking device in accordance with claim 1 wherein said lock body defines a cap at said first end thereof, said cap being generally cylindrical in shape and having a diameter which is greater than a diameter of a remaining portion of said lock body.
 4. The locking device in accordance with claim 1 wherein said head of said pin is generally triangular in shape.
 5. The locking device in accordance with claim 1 wherein said pin defines at least one slot at said second end of said pin and wherein said lock arm has at least one second tab extending therefrom which engages said at least one slot in said pin when said lock arm is mounted to said pin.
 6. A locking manhole cover comprising: a generally circular manhole cover having a top side and a bottom side and a generally circular perimeter, said manhole cover having a passage there through; and a cover lock connected to said manhole cover, said cover lock comprising: a lock body, said lock body located at least partially within said passage through said manhole cover, a top end of said lock body located at said top side of said manhole cover and a bottom end of said lock body located at said lock body side of said manhole cover; a pin located in a passage through said lock body, said pin having a head located at said top end of said lock body and accessible from said top side of said manhole cover; and a lock arm connected to a bottom end of said pin opposite said head thereof, said lock arm located at said bottom end of said lock body at said bottom side of said manhole cover, said lock arm rotatable relative to said lock body between a first position and a second position.
 7. The locking manhole cover in accordance with claim 6 wherein said lock body defines a cap at said top end thereof, said cap supported by said manhole cover and positioned in a portion of said manhole cover such that a top of said cap is generally flush with said top side of said manhole cover.
 8. The locking manhole cover in accordance with claim 6 including a nut having threads engaging mating threads on an exterior of said lock body, said nut located on said lock body at said bottom side of said manhole cover.
 9. The locking manhole cover in accordance with claim 6 wherein said lock body defines at least one slot in said bottom end thereof and where said lock arm includes at least one outwardly extending tab configured to engage said at least one slot when said lock arm is in said first position, and to not engage said at least one slot when said lock arm is in said second position.
 10. The locking manhole cover in accordance with claim 6 wherein said head of said pin is generally triangular in shape.
 11. The locking manhole cover in accordance with claim 6 wherein said pin defines a slot in said bottom end thereof and wherein said lock arm defines at least one outwardly extending tab which is positioned in said slot in said pin, preventing rotating of said lock arm relative to said pin when said lock arm is connected to said pin.
 12. The locking manhole cover in accordance with claim 6 including means for biasing said pin upwardly relative to said lock body.
 13. A method of selectively locking a manhole cover to a frame comprising the steps of: providing a cover with a cover lock, said cover having a top side and a bottom side and a generally circular perimeter, said cover having a passage there through and said cover lock comprising a lock body, said lock body located at least partially within said passage through said cover, a top end of said lock body located at said top side of said cover and a bottom end of said lock body located at said lock body side of said cover, a pin located in a passage through said lock body, said pin having a head located at said top end of said lock body and accessible from said top side of said cover, and a lock arm connected to a bottom end of said pin opposite said head thereof, said lock arm located at said bottom end of said lock body at said bottom side of said cover, said lock arm rotatable relative to said lock body between a first position and a second position; locating said cover on a supporting structure, said supporting structure having at least one portion located under said cover which extends outwardly; engaging said head of said pin with a tool; rotating said pin from a first position to a second position, causing said lock arm to rotate from a first unlocked position to a second locked position in which at least a portion of said pin is located beneath said at least one outwardly extending portion of said supporting structure; and permitting said lock arm to move upwardly into engagement with said lock body.
 14. The method in accordance with claim 13 wherein said lock body has at least one slot located at a bottom thereof and said lock arm has at least one tab extending outwardly therefrom and said step of permitting said lock arm to move upwardly includes said at least one tab moving into said at least one slot. 